策略模式+Spring消除if-else

た入场券 2022-11-26 15:58 210阅读 0赞

为了消除if-else  
最近想把消息服务的几种下发方式通过策略模式整理一下,因为用的spring,直接上代码

public interface IMessageService { 
    
        /** * 定位策略的key * * @return key */
        String fetchkey();
    
    	//具体执行
        void sent(String msg);
    }

@Component
    public class IEmailServiceImpl implements IMessageService { 
    
        private final Logger logger = LoggerFactory.getLogger(this.getClass());
    
        @Autowired
        EmailUtil emailUtil;
    
        @Override
        public String fetchkey() { 
            return "msg_handle_email";
        }
    
        @Override
        public void sent(String msg) { ...}

@Component
    public class ISmsServiceImpl implements IMessageService { 
    
        @Autowired
        SmsUtil smsUtil;
        @Autowired
        RedisTemplate redisTemplate;
    
        private final Logger logger = LoggerFactory.getLogger(this.getClass());
    
        @Override
        public String fetchkey() { 
            return "msg_handle_sms";
        }
    
        @Override
        public void sent(String msg) { ...}

@Component
    public class IWechatServiceImpl implements IMessageService { 
    
        private final Logger logger = LoggerFactory.getLogger(this.getClass());
    
        @Autowired
        AppWXUtil appWXUtil;
    
        @Override
        public String fetchkey() { 
            return "msg_handle_wechat";
        }
    
        @Override
        public void sent(String msg) { ...}

@Component
    public class MessageHandler implements InitializingBean, ApplicationContextAware { 
    
        private Map<String, IMessageService> messageServiceMap = new ConcurrentHashMap<>(8);
    
        private ApplicationContext applicationContext;
    
        /** * 将IMessageService的类都按照定义好的规则（fetchKey），放入messageServiceMap中 */
        @Override
        public void afterPropertiesSet() { 
            Map<String, IMessageService> matchBeans = applicationContext.getBeansOfType(IMessageService.class);
            matchBeans.forEach((key, value) -> messageServiceMap.put(value.fetchkey(), value));
        }
    
        /** * 注入applicationContext * * @param applicationContext ac * @throws BeansException e */
        @Override
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { 
            this.applicationContext = applicationContext;
        }
    
        /** * 通过key获取对应的策略实现 * * @param key key * @return IMessageService */
        public IMessageService getMessageSender(String key) { 
            return messageServiceMap.get(key);
        }

将来如果需要扩展起来也非常容易：只需在impl目录下添加策略类，定义好对应的策略key，就可以了

关键在于 MessageHandler,它实现了InitializingBean和ApplicationContextAware两个接口。

**实现了ApplicationContextAware接口的类，可以注入applicationContext实例**

实现了ApplicationContextAware接口的类，会重写方法, 可以通过此方法，让当前类拿到applicationContext实例。

public void setApplicationContext(ApplicationContext applicationContext) throws BeansException

或者通过注解获取;

@Autowired
    private ApplicationContext applicationContext；

实现了InitializingBean的类，会在实例化Bean的时候，调用其afterPropertiesSet方法。

在实例化此Bean的时候，我们调用了afterPropertiesSet方法，方法里通过applicationContext对象，拿到所有IMessageService类型的类。然后将每个策略类fetchKey结果作为key，策略类本身作为value，存储到变量messageServiceMap中了。然后当要使用的时候，直接调用getMessageSender方法，根据key来获取策略类。